What does the cryptic crossword clue "Exceptional clue … (6)" mean?

The definition is "double-definition". The wordplay uses a charade (building blocks). SIGNAL (synonym of "clue ..."); definition: "Exceptional" The answer is SIGNAL.

Exceptional clue … (6)

Telegraph #30327 | 1 Across | 2023-06-15 flower

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Times Cryptic #29266 (2025-06-26)